WP: get images from unique parents

<?php
/*
   A function I use to quickly get a total of $limit-images (attachments), each from a unique parent post.
   Heavily used over at http://game.hgo.se/
*/
function ulfben_get_post_images(
    $number_of_posts = 5,
        $category_filter = '66', //comma delimited list of category IDs
        $order_by = 'RAND()', //post_date DESC or what have you.
    $size = 'thumbnail' //'thumbnail', 'medium', 'large' or 'full' or an array of width and height, e.g. array(32,32)
 ){
    global $wpdb;
    $limit = (intval($number_of_posts) <= 0) ? 1 : $number_of_posts;
    $images = $wpdb->get_results(
        "SELECT SQL_SMALL_RESULT DISTINCT $wpdb->posts.post_parent, $wpdb->posts.ID
        FROM $wpdb->posts
        WHERE $wpdb->posts.post_parent IN (
                SELECT SQL_SMALL_RESULT DISTINCT $wpdb->posts.ID
            FROM $wpdb->posts
                LEFT JOIN $wpdb->term_relationships ON ($wpdb->posts.ID = $wpdb->term_relationships.object_id)
                LEFT JOIN $wpdb->term_taxonomy ON ($wpdb->term_relationships.term_taxonomy_id = $wpdb->term_taxonomy.term_taxonomy_id)
            WHERE $wpdb->term_taxonomy.taxonomy = 'category' AND $wpdb->term_taxonomy.term_id IN({$wpdb->escape($category_filter)})
            AND $wpdb->posts.post_type = 'post'
            AND $wpdb->posts.post_status = 'publish'
            AND $wpdb->posts.post_password = ''
        )
        AND $wpdb->posts.post_type = 'attachment'
        AND $wpdb->posts.post_mime_type IN ('image/jpeg', 'image/gif', 'image/png')
        ORDER BY {$order_by}
        LIMIT {$limit};"
    );
    $selection = array();
    foreach($images as $img){
        $imgurl = wp_get_attachment_image_src($img->ID, $size);
        if($imgurl === false){continue;} //the image doesn't exist?
        $img_width = $imgurl[1];
        $img_height = $imgurl[2];
        $imgurl = $imgurl[0];
        $selection[] = array(
            'post_url' => get_permalink($img->post_parent),
            'post_title' => wp_specialchars(get_the_title($img->post_parent)),
            'post_id' => $img->post_parent,
            'img_id' => $img->ID,
            'img_src' => $imgurl,
            'width' => $img_width,
            'height' => $img_height
        );
    }
    return $selection;
}
function ulfben_print_post_images(
    $number_of_posts = 5, //number of posts
    $image_attributes = '',
        $category_filter = '66', //comma delimited list of category IDs
        $order_by = 'RAND()', //{$wpdb->posts}.post_date DESC or what have you.
    $size = 'thumbnail' //'thumbnail', 'medium', 'large' or 'full' or an array of width and height, e.g. array(32,32)
    ){
    $images = ulfben_get_post_images($number_of_posts, $category_filter, $order_by, $size);
    foreach($images as $image){
        echo "<a href='{$image['post_url']}' title='".esc_attr($image->post_title)."'><img src='{$image['img_src']}' alt='{$info}' {$image_attributes}/></a>";
    }
}
?>